Recent studies indicate that the human papillomavirus (“HPV”) is associated with a significant fraction of cervical, head/neck, anal, and schistosomiasis-associated bladder cancers. Cervical and anal cancers are almost uniformly associated with HPV infection. A recent review of published reports found the overall prevalence of HPV DNA in head and neck tumors to be 35%. More recently some researchers have used quantitative PCR (“QPCR”) to confirm these findings in a large study of 253 tumor samples, where they detected HPV DNA in 25% of specimens. HPV is also associated with anal dysplasias and cancers. Other researchers have found that nearly 50% of schistosomiasis-caused bladder cancers had HPV DNA by in situ hybridization.
HPV types 16 and 18 are among the ‘high risk’ viral types since their presence is associated with preneoplastic lesions and carcinomas. In contrast, the ‘low risk’ types, most commonly HPV types 6 and 11, are typically associated with benign lesions. The oncogenic potential of HPV is principally due to two viral oncoproteins, E6 and E7. Differences in oncogenic potential among HPV types have been attributed to type-specific differences in the E6 and E7 proteins. The E6 protein of oncogenic HPV strains has been shown to interact with the p53 protein and promote its degradation via a ubiquitin-dependent pathway. The E7 oncoprotein can, similarly, complex with the retinoblastoma (Rb) protein and inactivate it. Both p53 and Rb are important tumor suppressor genes whose products regulate the cell cycle, orchestrate DNA repair processes, and are involved with programmed cell death or apoptosis. Disruption of these tumor suppressor proteins by HPV leads to propagation of mutational changes and cell immortalization.
The technique of examining serum DNA for abnormal genomes of cancer cells has been studied as a potential molecular test for cancer. Although some researchers found that the TaqMan quantitative PCR method could detect HPV DNA in serum from some patients with head/neck and cervical cancers, HPV DNA was not detectable by this technique in serum and other biological locations in sufficient amounts to be useful in most subjects as a clinical tool.
As examples of current limitations, problems with the current standard of care for HPV testing, the Digene test [1], include:
1. The Digene test cross-reacts non-specifically with HPV types other than the known pathogenic types [2]. Thus there are unavoidable false positives with the Digene test;
2. The Digene test requires at least several thousand HPV molecules to read as positive [1]. This requirement prevents screening of serum and/or blood where a smaller number of molecules are present; and
3. The Digene test does not reveal which HPV type is found in the cervix ThinPrep. This becomes important as non-pathogenic types of HPV can yield false positive results if the types of HPV responsible for a signal are not identified.
In view of these and other limitations and shortcomings in the art, an unmet need remains for systems, methods, and compositions for the detection and identification of individual HPV species in biological samples at levels not detectable by currently available methods.